To produce oil and gas from a hydrocarbon reservoir, a wellbore is first drilled through geological formations. During drilling operations, specially designed reservoir drilling fluids may have various additives, including biologically-derived polymers and bridging solids that lubricate the drill bit and remediate fluid loss into the formation. Drilling fluid additives are often formulated such that formation damage caused by the accumulated drilling fluids may be reversible, because the additives are soluble or breakable upon contact with a suitable breaker fluid, which may include acids, oxidizers, or enzymes, for example.
Once the wellbore is generated in the hydrocarbon reservoir, production tubing and/or screens may be emplaced within the wellbore and placed within an interval of the formation prior to hydrocarbon production. During production, sand control methods and/or devices are used to prevent sand particles in the formation from entering and plugging the production screens and tubes in order extend the life of the well. Sand control methods may include gravel packing in which the annular space between the wellbore and the production screens is filled with specially sized gravel packing sand.
Following drilling operations and prior to introduction of the sand or gravel for the gravel pack, the hydrocarbon-bearing formation may contain a substantially impermeable filtercake created by the reservoir drilling fluid. This thin and impermeable filtercake may prevent the gravel pack fluid from entering the formation, and may result in gravel pack failure. Moreover, after gravel pack emplacement, the filtercake existing between the gravel pack sand and the formation may require removal before the flow of hydrocarbon may be initiated. Without the removal of the filtercake, plugging of the production screen by the filtercake could occur, impairing production.
Various chemicals, breakers, and mechanical devices have been developed to remove filtercakes during gravel packing operations. For example, acids may be delivered to soak the gravel pack sand and filtercake. Here, the goal is to dissolve the acid-soluble and acid-breakable components in the filtercake and remediate the damaged formation.
Other breakers, such as oxidizers and enzymes, may also be delivered to destroy oxidizer- and enzyme-breakable organic components. They may not be as effective in destroying acid-soluble and acid-breakable inorganic components in the filtercake, such as calcium carbonate. As a result, acid-soluble and breakable components may remain behind the gravel pack sand and cause impairment during the production of the well. Secondly, many oxidizing breakers have compatibility issues with certain brines and may react with the brine and create undesirable by-products, such as Cl2 and Br2 gases. This reaction can occur even before the breakers are pumped down to attack the filtercake. Third, in addition to brine compatibility issues, enzyme breakers may also have reduced activity outside of the optimal temperature range for the given enzyme. For example, enzyme breakers may lose reactivity in highly concentrated divalent brines or at temperatures above 93° C. (200° F.).
The above filtercake breakers are often pumped separately after the gravel pack sand has been set. They are not pumped during the gravel pack operation because they can create precarious conditions for the operation. For instance, the acid-based breakers can destroy the filtercake during gravel pack operations, which may result in high fluid loss and premature failure in the gravel pack operation. Similarly, pumping oxidizers and enzyme breakers with gravel pack sand may cause inconsistent application of oxidizers and enzyme breakers to the filtercakes.